Apolipoprotein A-IV is a lipid binding protein found in the intestine, which plays a role in the absorption of dietary fat. A genetic variation, apo A-IV-2, has been found to affect how much dietary cholesterol changes cholesterol in the blood. We studied two groups of subjects, one group which carried the genetic variation, A-IV-2, which can affect dietary cholesterol absorption, and a normal control group, to determine how rapidly they could metabolize fat.